As a linear actuator that lineally moves a displacing body is known e.g., a device provided with a motor (rotation-typed actuator), a decelerating unit that decelerates and transmits rotational driving force of the motor, and a rack-and-pinion unit that converts; the rotary motion to linear motion.
However, there is a problem that it is hard to allow the actuator to be more miniaturized, lighter and particularly thinner, since the above-mentioned conventional linear actuator needs to have the decelerating unit and the motor of the actuator is bulky.
Further, the configuration of the actuator is complicated, and there occurs a big noise.
Furthermore, there is also a problem that an electromagnetic noise that the motor occurs might provide harmful affects against any other equipment.
Here, Japanese Laid-open Patent Application No. 2001-161084 discloses a linear-moving mechanism having a cam mechanism that converts rotary motion of a rotor, which is driven by an ultrasonic motor, to linear motion of a displacing body.
However, driving force (driving torque), a driving speed, and a driving efficiency of the linear-moving, mechanism disclosed in the above application have been insufficient in view of a configuration of the ultrasonic motor to be used.
As the other one of defects of the above mentioned linear-moving mechanism, since frictional force is provided between the rotor and a vibrating element by applying pushing force against the rotor in a direction of an shaft of the rotor so that the driving force is obtained, in a case where the pushing force in the direction of the shaft of the rotor is changed, the driving characteristic undergoes great change. In other words, as shown in FIGS. 1 and 2 of the above application, in such a system in which a displacing body 14 abuts on a cam (its outer circumferential surface) 13 from a lateral direction of a rotor 4, pushing force in the axle direction of the rotor 4 is greatly affected by such a lateral pressure added from the displacing body 14 onto the cam 13. Thus, the driving characteristic undergoes great change. On the other hand, as shown in FIG. 4 of the above application, in a system in which the displacing body 14 abuts on the cam (its lateral face) 13 from the direction of the shaft of the rotor 4, pushing force in the shaft of the rotor 4 is directly affected thereto. Thus, the driving characteristic also undergoes great change.